1. Field of the Invention
The present invention relates to a rotation detector and rotation controller using this detector. In particular, the present invention is preferably applicable to a rotary encoder, which detects the rotation position of the disk, the amount and direction of the displacement of the rotation position, the rotation speed and acceleration and the like, by illuminating a radial diffraction grating and a code pattern on a disk attached to a relative rotation object with a light beam, and by detecting a modulated signal light obtained therefrom. The rotation detector and controller are applicable to a device, such as a motor with an encoder, which makes the object rotationally move by controlling the current and direction of the driving unit such as an AC motor and the like.
2. Related Background Art
Incremental rotary encoders have been used for high precision measurement of information on the rotation of the object, such as displacement, speed, acceleration and the like. Further, absolute rotary encoders, which detect the absolute rotation position of the rotor in the motor, have been used for brushless motors, such as AC motors. Therefore, combination rotary encoders which can obtain both signals are employed for controlling the rotation position of the object using AC motors and the like.
Conventional high precision incremental encoders detecting the displacement, as shown in Japanese Patent Publication Nos. 58-26002 and 58-45687 on the object, output incremental encoder signals by illuminating a monochrome light beam in which fine grating elements are recorded on the scale, by making periodic changes of the amount of the light with grating movement by means of the interference between at least two kinds of diffracted light among a plurality of diffracted light obtained therefrom, and by detecting a photoelectric element.
Further, conventional absolute rotary encoders, as disclosed in U.S. Pat. No. 3,591,841, have a structure which outputs the absolute rotation position of the disk, by forming a plurality of transmittable/non-transmittable or reflective/nonreflective patterns, such as grey code patterns, on the circuits, having different radii, on the rotation disk, so that only one combination of the codes exists in one rotation, and by detecting transmitted or reflected light at the specified position on each circuit. A typical absolute encoder for the motor outputs the position between the rotor and stator in the motor, by forming a plurality of transmittable/non-transmittable or reflective/nonreflective patterns, such as grey code patterns, on the circuits, having different radii, on the rotation disk, so that only M combinations of the codes exists corresponding to the structure of the motor, the number of the pole M, and by detecting the transmitted or reflected light at the specified position on each circuit.
In recent years, although a more compact encoder, for example, a disk having a diameter of 10 millimeters, has been required, it is difficult to miniaturize the combination encoder based on the different principles as described above. The miniaturization, in which two optical systems based on the different detection principles are placed together and each system is intended to miniaturize, has a limitation and some problems as follows: A plurality of light sources are separately required for the absolute encoder portion and the incremental encoder portion so that heat generation increases with the increased current consumption, and the structure becomes more complicated due to the increased number of parts required. In particular, since a device having an incremental encoder portion using a grating interference system requires a certain size so that the accuracy of the interference can be maintained, it is even more difficult to miniaturize this when another rotation detector is provided together.